LINQ查询Concat值到类型字符串列表

Question

有没有更有效的方法来解决这个问题？

List<String> lstReferences = (from f in 
                            (from section in courseSectionToCreate.SectionsToAdd
                                select new {
                                            ReferenceNumber = section.Course.CourseNumber.Substring(0, 5) + "." +
                                                section.Course.CourseNumber.Substring(5) + "." +
                                                section.Session + "." +
                                                section.Year + "." +
                                                section.SectionNumber + ";"
                                            })
                            select f.ReferenceNumber).ToList();

strReferenceNumber = lstReferences.Aggregate((a, b) => a + ", " + b);

Answer 1

是的，你绝对不想在这里使用Aggregate。那是O(n^2)（Schlemiel the Painter's algorithm）。代替：

string referenceNumber = String.Join(", ", lstReferences);

这样做会更好，因为String.Join会在内部使用StringBuilder。

Answer 2

怎么样：

var lstReferences = from section in courseSectionToCreate.SectionsToAdd     
                    let courseNumber = section.Course.CourseNumber                           
                    let toJoin = new object[] 
                    { 
                       courseNumber.Substring(0, 5),
                       courseNumber.Substring(5),
                       section.Session,
                       section.Year,
                       section.SectionNumber
                    }
                    select string.Join(".", toJoin) + ";" 

var strReferenceNumber = string.Join(", ", lstReferences); 

Answer 3

您可以用以下内容替换所有内容：

var strReferenceNumber =
    String.Join(", ",
        courseSectionToCreate.SectionsToAdd.Select(s =>
            String.Join(".", 
                s.Course.CourseNumber.Substring(0, 5),
                s.Course.CourseNumber.Substring(5),
                s.Session,
                s.Year,
                s.SectionNumber) + ";"
        )
    );